Abstract

Background

The most recent strategy for schistosomiasis control in the People's Republic of China
aims to reduce the likelihood of environmental contamination of schistosome eggs.
Despite considerable progress, it is believed that achievements would be further consolidated
with additional intermediate host snail control measures. We provide an empirical
framework for discerning the relative contribution of intrinsic effects (density feedback)
from other extrinsic drivers of snail population dynamics.

Methods

We set up experiments in two study locations to collect reproduction data of Oncomelania hupensis, the intermediate host snail of Schistosoma japonicum. We applied a set of four population dynamic models that have been widely used to
study phenomenological time-series data to examine the properties of demographic density
feedback patterns from abundance data. We also contrasted the obtained results with
the component feedback of density on survival rate to determine whether adult survival
was the principal driver of the demographic feedback observed.

Results

Demographic density feedback models (Ricker- and Gompertz-logistic) accounted for
> 99% of Akaike's information criterion model weight, with the Gompertz ranking highest
in all O. hupensis population groups. We found some evidence for stronger compensatory feedback in the
O. hupensis population from Sichuan compared to a Jiangsu population. Survival rates revealed
strong component feedback, but the log-linear relationships (i.e. Gompertz) had less
support in the demographic feedback analysis.

Conclusions

Our findings indicate that integrated schistosomiasis control measures must continue
to reduce parasite abundance further because intermediate host snail populations tend
to grow exponentially at low densities, especially O. hupensis populations in mountainous regions. We conclude that density feedback in adult survival
is the principal component contribution to the demographic phenomenon observed in
the population fitness (r)-abundance relationship.